1. Field of the Invention
The present invention relates to a novel dichroic dye for color liquid crystals. In particular, it relates to a dichroic dye for color liquid crystals to be used, for example, in a guest-host liquid crystal display (hereinafter referred to as G-HLCD) or the like.
2. Description of the Prior Art
As dichroic dyes to be used in liquid crystals are known those having azo, azomethine or antroquinone structures.
Dichroic dyes to be used in liquid crystals have to meet various requirements. Of the requirements to be met by the dichroic dyes, the followings are of particular importance.
(1) To have a high dichroic ratio (hereinafter referred to as CR); PA1 (2) To have a high molecular extinction coefficient (hereinafter referred to as .epsilon.); PA1 (3) To have a long service life (i.e., to have an excellent resistance to light); and PA1 (4) To have a high solubility (hereinafter referred to as S).
However, the service lifes of azo and azomethine dyes are generally short although their .epsilon. values are generally high. On the other hand, antraquinone dyes, although their service lifes are generally long, generally have low CR and .epsilon. values. Accordingly, few dichroic dyes have been known that satisfy all the requirements (1), (2), (3) and (4) described above.
The present inventors had previously found that dyes represented by the following General Formula (1): ##STR2## in which Dye 1 and Dye 2 each represents a group of atoms necessary to form a linear dye structure containing an azo, azomethine or ester group, have not only large CR and .epsilon. values, but also a long service life (see Japanese Patent Application Nos. 98,057/83 and 130,364/83).
However, it was later found that the dichroic dyes represented by the above General Formula (1) have a S value more or less lower than those of previously known dyes.